1. Field of the Invention
The present invention relates to a solid-state imaging device, a method of manufacturing the same, and an electronic apparatus including the solid-state imaging device.
2. Description of the Related Art
Solid-state imaging devices are classified roughly into charge transfer solid-state imaging devices typified by a charge-coupled device (CCD) image sensor and amplification type solid-state imaging devices typified by a complementary metal oxide semiconductor (CMOS) image sensor.
Typically, a CCD solid-state imaging device has an imaging region including a plurality of light-sensing sections, i.e., photodiodes serving as photoelectric conversion elements, which are two-dimensionally arrayed, and a vertical transfer register section which has a CCD structure and which is disposed for each column of photodiodes. The CCD solid-state imaging device further includes a horizontal transfer register section which has a CCD structure and which transfers signal charges from the imaging region in the horizontal direction, an output section, peripheral circuits constituting a signal processing circuit, etc.
Typically, a CMOS solid-state imaging device has an imaging region in which a plurality of pixels, each including a photodiode serving as a photoelectric conversion element constituting a light-sensing section and a plurality of pixel transistors (MOS transistors), are two-dimensionally arrayed, and a peripheral circuit section which is disposed in the periphery of the imaging region and which performs signal processing, etc.
Concerning these solid-state imaging devices, with the miniaturization of pixels, in order to improve the light collection efficiency of incident light, a structure having a waveguide for each photodiode has been proposed, the waveguide including a cladding layer and a core layer having different refractive indices. Solid-state imaging devices having a waveguide function are disclosed, for example, in Japanese Unexamined Patent Application Publication Nos. 2000-150845, 2003-324189, 2004-221532, 2005-294749, and 2006-86320, etc.
FIGS. 27 to 29 show an example of a CCD solid-state imaging device according to the related art. FIG. 27 is a plan view showing a main portion of an imaging region, FIG. 28 is a cross-sectional view taken along the line XXVIII-XXVIII of FIG. 27, and FIG. 29 is a cross-sectional view taken along the line XXIX-XXIX of FIG. 27. Referring to FIG. 27, in a CCD solid-state imaging device 100, generally, square photodiodes (PDs) constituting light-sensing sections 101 are two-dimensionally arrayed, and a vertical transfer register section 102 which has a CCD structure and which transfers signal charges in the vertical direction is disposed for each column of light-sensing sections. The vertical transfer register section 102 includes a buried transfer channel region 103 and a plurality of transfer electrodes disposed thereon with a gate insulating film therebetween. In this example, three transfer electrodes (transfer electrodes 104, 105, and 106) are disposed so as to correspond to one photodiode (PD) constituting a light-sensing section 101, the transfer electrodes 104, 105, and 106 being composed of a first-layer polysilicon film.
The transfer electrodes 104 and 106 are respectively continuously formed so as to extend in the horizontal direction along the space between the vertically adjacent light-sensing sections 101 such that the corresponding electrodes in the vertical transfer register sections 102 are connected to one another. In the meantime, the transfer electrodes 105 which also serve as readout electrodes are independently formed like islands, and thus, are connected to connecting conductive layers 107 composed of a second-layer polysilicon film. The connecting conductive layers 107 have strip portions 107B disposed on the transfer electrodes 104 and 106, which extend between the vertically adjacent light-sensing sections 101, with an insulating film therebetween, and extending portions 107A integrated with the strip portions 107B and extending over the transfer electrodes 105. The extending portions 107A are connected to contact portions 108 of the transfer electrodes 105 in the corresponding vertical transfer register sections 102.
As shown in the cross-sectional views of FIGS. 28 and 29, on a first conductivity type (e.g., n-type) semiconductor substrate 111, a first semiconductor well region 112 of a second conductivity type (p-type) is disposed, and photodiodes (PDs) constituting light-sensing sections 101 are disposed in the p-type first semiconductor well region 112. Each photodiode (PD) includes an n-type semiconductor region 113 and a p-type semiconductor region 114 which suppresses dark current. Furthermore, n-type buried transfer channel regions 115 and p+ channel stop regions 116 are disposed in the p-type first semiconductor well region 112. A p-type second semiconductor well region 117 is disposed directly under each buried transfer channel region 115.
Transfer electrodes 104 to 106 composed of a first-layer polysilicon film are disposed on the buried transfer channel regions 115 with a gate insulating film 118 therebetween, and connecting conductive layers 107 composed of a second-layer polysilicon film, which are connected to the island-like transfer electrodes 105 through an insulating film 119, are disposed. A light-shielding film 120 is disposed so as to cover, excluding the photodiodes (PDs), the transfer electrodes 104 to 106 and the connecting conductive layers 107 with the insulating film 119 therebetween. An insulating film 121, for example, composed of a silicon oxide film, and an antireflection film 122, for example, composed of a silicon nitride film, are disposed on the surfaces of the photodiodes (PDs) not provided with the light-shielding film 120.
A waveguide 124 is disposed above each photodiode (PD) so that incident light can be effectively collected onto the photodiode (PD). The waveguide 124 includes a core layer 125 having a high refractive index, for example, composed of a silicon nitride film, and a cladding layer 126 surrounding the core layer 125 and having a low refractive index, for example, composed of a silicon oxide film.
An on-chip color filter 128 is disposed further thereon with a passivation film 130 and a planarizing film 127 on the passivation film 130 therebetween, and on-chip microlenses 129 are disposed on the on-chip color filter 128.
The transfer electrode 105 and the connecting conductive layer 107 can have the same width as shown in FIG. 30, or the width of the connecting conductive layer 107 can be set smaller than the width of the transfer electrode 105 as shown in FIG. 31. In either case, the transfer electrode 105 and the connecting conductive layer 107 are formed symmetrically with respect to the axis O.
FIGS. 32A to 32C and FIGS. 33D and 33E show steps in a method of manufacturing a solid-state imaging device 100 according to the related art, in particular, a process of fabricating a waveguide. In each drawing, the left portion corresponds to a cross-section taken along the line XXVIII-XXVIII of FIG. 27 (in the horizontal direction), and the right portion corresponds to a cross-section taken along the line XXIX-XXIX of FIG. 27 (in the vertical direction).
First, as shown in FIG. 32A, transfer electrodes 104 to 106 are formed, with a gate insulating film 118 therebetween, on a semiconductor substrate 111 in which photodiodes (PDs), buried transfer channel regions 115, channel stop regions 116, etc. have been formed. Furthermore, connecting conductive layers 107, some of which are connected to the transfer electrodes 104, are formed thereon with an insulating film 119 therebetween, and a light-shielding film 120 is formed thereon with the insulating film 119 therebetween. To simplify the drawings, the buried transfer channel regions 115, the channel stop regions, etc. are omitted therefrom.
Next, as shown in FIG. 32B, a cladding material film 126A (composed of a low-refractive-index material) for forming a cladding layer of waveguides is formed over the entire surface of the light-shielding film 120 and the inside of the openings corresponding to the photodiodes 101. The cladding material film 126A can be formed, for example, using silicon oxide (SiO2), such as the one formed by heat-treating borophosphosilicate glass (BPSG), followed by ref lowing. At this time, as shown in FIG. 32B, the BPSG layer is formed with a large thickness. Then, the surface of the BPSG layer is planarized, for example, using chemical mechanical polishing (CMP), dry etching, or the like.
Next, as shown in FIG. 32C, a resist mask 132 having openings 132a at positions corresponding to the photodiodes 101 is formed on the cladding material film 126A using a lithographic technique.
Next, as shown in FIG. 33D, the cladding material film 126A is dry-etched using the resist mask 132, thereby to form recesses 133 which extend to an antireflection film 122. Thereby, a cladding layer 126 composed of the cladding material film 126A is formed on the inner walls of the recesses 133.
Next, as shown in FIG. 33E, by embedding a material (high-refractive-index material) having a higher refractive index than the cladding layer 126 in the recesses 133, a core layer 125 is formed. The core layer 125 is also formed on surfaces other than the recesses 133. In such a manner, waveguides 124 each including the core layer 125 and the cladding layer 126 are formed.